Prior to this invention various seal ring constructions have been used to prevent leakage of fluid between parts of a pipeline or other fluid-receiving system. For example, a particularly effective seal ring construction is disclosed in U.S. Pat. No. 3,625,552 which issued to George A. Mahoff on Dec. 7, 1971.
In order to establish a seal between male and female coupling parts with the Mahoff seal ring, special male and female or inner and outer formations are required for torsionally deflecting the seal ring. In the Mahoff patent, these formations are formed on the coupling parts and define a cavity for receiving the seal ring.
Each of the special, cavity-defining formations in the Mahoff assembly is defined by a cylindrical surface and by a conical surface which intersects the cylindrical surface to form a circumferentially extending corner. The cylindrical surfaces of the cavity-defining formations are overlapping, while the conical surfaces of the formations confront each other so that as the coupling parts are drawn axially together, the diagonally opposite corner edges of the seal ring slide along the formations to seat in the formations' corners. Further relative axial movement of the coupling parts toward each other then deforms the seal ring into a cone-shaped configuration in which the radial dimension of the seal ring is increased to cause the interference that produces the fluid tight seal.
Various parts requiring a seal, however, are not manufactured with the special cavity-defining formation which is needed for torsionally deflecting the Mahoff seal ring. Furthermore, it is not feasible or practical in some cases to machine or otherwise modify the part to form the required formation for engaging the seal ring. One solution to this problem is to custom build the part. But such a solution has the drawback of substantially increasing the cost of the assembly.